Distributed Collaborative Signaling in Full Duplex Wireless Transceivers

ABSTRACT

Two-way (full-duplex) wireless links in facilitating network management and improve network performance. Once aspect includes methods for network management using an overlaid network for control signaling. Another aspects include methods to facilitate practical realization and improve performance of some of the network information theoretic configurations, such as Space-Division Multiple Access (SDMA) in uplink and downlink, Interference Channel, and other forms of distributed collaborative signaling schemes. Another aspect includes methods to support cognitive wireless networks.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a non-provisional filing of, and claimsbenefit under 35 U.S.C. §119(e) from, U.S. Provisional PatentApplication Ser. No. 61/646,312, filed May 13, 2012, and U.S.Provisional Patent Application Ser. No. 61/771,815, filed Mar. 2, 2013,both of which are hereby incorporated herein by reference. In addition,this application is related to the following applications, all of whichare also incorporated herein by reference: Attorney docket 71500.US.03entitled Full Duplex Wireless Transmission with Self-InterferenceCancellation, filed on May 13, 2013, Attorney docket 71501.US.01entitled Wireless Transmission with Channel State Perturbation, filedMay 13, 2013, Attorney Docket 71502.US.01, entitled Full Duplex WirelessTransmission with Channel Phase-Based Encryption, filed May 13, 2013.

FIELD

The present disclosure relates to wireless communications. Inparticular, the present disclosure relates to systems and methods usingtwo-way (full-duplex) wireless links.

BACKGROUND OF THE INVENTION

A communication link (e.g. between node A and node B) with thecapability to support the connection in both directions at the same timeis called full-duplex, or two-way. In contrast, a link that can supportthe connection in only one direction at a time is called one-way orhalf-duplex.

Current wireless systems are one-way and rely on either separate timeslots (Time Division Duplex, TDD) or separate frequency bands (FrequencyDivision Duplex, FDD) to transmit and to receive. These alternativeshave their relative pros and cons, but both suffer from lack of abilityto transmit and to receive simultaneously and over the entire frequencyband. Full-duplex capability is particularly useful when severalwireless nodes share a frequency band, as it helps in managing theimpact of multi-user interference, maximizing spectral efficiency, andimproving network quality of service.

Point-to-point communications primarily concerns transmission between asingle transmitter and a single receiver, while networking concernsscenarios where more than two users share the channel. The impact offull-duplex links in point-to-point communications is limited todoubling the rate by providing two symmetrical pipes of data flowing inopposite directions. This affects the point-to-point throughput with nodirect impact on networking. In contrast, in multi-user wirelesssystems, due to the nature of transmission that everyone hears everyoneelse, full-duplex capability provides new ways to facilitate sharing ofa common spectrum.

A basic feature of wireless transmission is that the transmission mediais shared among all users and everyone hears everyone else. This featurecan cause harmful effects in terms of multi-user interference andnormally necessitates sophisticated network management. Full-duplexcapability with support for asynchronous clients provides the means tobenefit from the same basic feature of wireless transmission andfacilitate network management.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The accompanying figures, where like reference numerals refer toidentical or functionally similar elements throughout the separateviews, together with the detailed description below, are incorporated inand form part of the specification, and serve to further illustrateembodiments of concepts that include the claimed invention, and explainvarious principles and advantages of those embodiments.

FIGS. 1 and 2 show block diagrams of a communication network in which anaccess point (AP) is communicating with multiple clients withfull-duplex links to each client and where the access point of FIG. 2communicates with multiple clients using OFDMA for sharing the bandwidthamong users with full-duplex link over OFDM tone and with support formultiple transmit and multiple receive antennas;

FIG. 3 is a block diagram showing cooperative communications 20 betweena central wireless communications device 200 and K other devices, 201,202, . . . (Unit₁-Unit_(K));

FIG. 4 depicts block diagrams showing cooperative communication inaccordance with one example. Unit A has a message intended to be sent toUnit A′ and Unit B has a message intended to be sent to Unit B′.

FIG. 5 is a flowchart showing a method with operations 400 for awireless communication device for establishing and/or handlingcommunications over a Low Throughput Overlaid (LTO) channelasynchronously and in parallel (i.e. with overlap in time and frequency)with communications over a Higher Throughput Main (HTM) data channel inaccordance with one embodiment;

FIG. 6 shows a schematic view of units operating in the same frequencyband, which filter and super-impose/forward the signal received fromeach other to cancel (pre-compensate) the interference at their intendedreceiver;

FIG. 7 shows a more detailed schematic view of units operating in thesame frequency band, which filter and super-impose/forward the signalreceived from each other to cancel (pre-compensate) the interference attheir intended receiver.

Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale. For example, the dimensions of some of the elements inthe figures may be exaggerated relative to other elements to help toimprove understanding of embodiments of the present invention.

The apparatus and method components have been represented whereappropriate by conventional symbols in the drawings, showing only thosespecific details that are pertinent to understanding the embodiments ofthe present invention so as not to obscure the disclosure with detailsthat will be readily apparent to those of ordinary skill in the arthaving the benefit of the description herein.

DETAILED DESCRIPTION OF THE INVENTION

Methods are disclosed to benefit from full-duplex capability to simplifypractical implementation of network structures, simplify networkmanagement, or improve network performance. This includes a traditionalnetwork structure, as well as some basic information theoretic setups,such as space division multiple access (SDMA) in down-link (MIMObroadcast) and in the uplink (MIMO multiple access), cooperativesignaling towards reducing multi-user interference, and interferencechannel. The methods mat be explained in terms of using OFDMA formulti-user multiplexing, similar concepts are applicable to other meansof multi-user multiplexing, such as CDMA, TDMA and SDMA.

Cognitive transmission is a method to improve spectral efficiency ofwireless networks by allowing secondary users to transmit over aspectrum primarily assigned to some primary users as long as thenegative side effect on the primary users in managed. One example is thecase of sharing a licensed spectrum with un-licensed users, which areallowed to transmit subject to causing zero or minimal interference tothe licensed users. In conventional half-duplex networks, it isdifficult to manage such a sharing of spectrum, as nodes inherentlycannot listen which transmitting. Even in FDD systems, although userscan listen while transmitting, they will not be able to manage theimpact of their transmission on the reception of the other users in thenetwork as reception and transmission are not in the same frequencyband. This can be further generalized to scenarios in which there areseveral classes of QoS, corresponding to several classes of users, or todifferent types of data within the same class, e.g., depending on delaysensitivity of data or being emergency information. This disclosureincludes strategies to handle the above scenarios. Primary users, orusers sending data of a higher QoS requirement, send a signature signalwhich will be immediately detected by the secondary users, or by userssending data with a lower QoS requirement. Such secondary users will becontinually listening and searching for such a signature. Once thesignature is detected, secondary users adjust their transmissionparameters accordingly, or stop their transmission altogether andcontinue with the remaining part at a later time when the networkbecomes once again available to them. Parameters of the periodic signalcan be used to identify different classes of users, or convey somecritical information.

To describe the systems and methods a basic setup is employed. For thispurpose, aspects relevant to supporting multiple clients and networkingare described assuming OFDMA. However, techniques herein will beapplicable if OFDMA is replaced by some other known alternatives, e.g.,CDMA, OFDM-CDMA, Direct Sequence (DS)-CDMA, Time-division MultipleAccess (TDMA), constellation construction/transmission in time withpulse shaping and equalization, Space Division Multiple Access (SDMA),and their possible combinations.

FIGS. 2 and 3 show block diagrams of respective full duplexcommunication networks 100A and 100B, albeit simplified, in which anaccess point (AP) (e.g. 104 or 108) is communicating with multipleclients (106A, 106 B 106C and 106D) with full-duplex links to eachclient. Access point 108 of FIG. 2 communicates with multiple clientsusing OFDMA for sharing the bandwidth among users with full-duplex linksover each OFDM tone and with support for multiple transmit and multiplereceive antennas 110 (e.g. N×N). Though described as access points, thecomponents 104 and 108 may be configured as base stations (BS) or othercommunication components such as relays, range extenders, wirelessterminals, and wireless nodes involved in ad hoc or wireless meshnetworks.

This disclosure encompasses systems and methods wherein signals forcontrol of Physical Layer (PHY) operations are communicated in parallelwith the flow of data. In particular, one of the nodes inserts pilots inits transmit signal to help in synchronizing distant nodes. As anotherexample, transmitting nodes can simultaneously listen to a commonsynchronizing pilot sent by an external nodes, such as a satellite, anduse it towards forming a coherent distributed/co-operative scheme, suchas Interference Alignment or distributed MIMO, with support for jointdetection of separately encoded messages. In particular, this techniquecan be applied to interference channel, and to MIMO multiple accesschannel. In the case of SDMA in MIMO broadcast channel, the central nodesends a pilot in downlink to synchronize all its client nodes, and eachof the client nodes uses part of its up-link channel to feedback itscorresponding channel state. In the case of SDMA in MIMO uplink, thecentral node sends a pilot in downlink to synchronize all its clientnodes.

FIG. 2 is a block diagram showing cooperative communications 200 betweena central wireless communications device 200 and K other devices(Unit1-UnitK). Central unit has M multiple antennas, typically whereM=K. There is established 2K virtual pipes of data/controlcommunications over the same time/frequency where control communicationsinclude reference for time/frequency/clock synchronization, channelgain/phase, information for user selection and channel inversion inSDMA, beam-forming vectors, beam-forming gains, channel matrix in MIMO,ARQ, power control, instruction for adaptive coding and modulation, etc.In SDMA down-link, main data flow is out of central unit, while in SDMAuplink most data flow is into the central unit. Common control is usedby all nodes in the network and in particular includes reference fortime/frequency/clock synchronization. Such a common reference fortime/frequency/clock enables all the units to be globally synchronized,instead of local synchronization, which is used in traditionalalternatives using half-duplex links. This is particularly important inthe SDMA uplink, in which case all transmitting nodes can locally dealwith any mismatch they may have with the central receiving node prior totransmission, and this can be achieved without the need for feedback.Note that in traditional half-duplex links such mismatches are usuallymeasured and compensated in the receiver side. This would not bepossible in the SDMA uplink due to the reason that the common receiverwould usually have different mismatches with different transmitters andconsequently would not be able to compensate for all of them. If SDMAuplink is based on half-duplex links, the only option would be tofeedback the measured mismatches to their respective transmitting nodesto be compensated prior to transmission. However, this would requirecomplicated signaling and use of feedback. These problems are avoidedusing full-duplex links and methods explained above. Although thisfeature is explained in terms of SDMA, similar strategy could be used tosolve similar problems in the case of interfering nodes by enablingglobal synchronization at the transmitters' sides.

It is desirable that new clients, through sending request-to-joinsignal, can join an existing network without prior co-ordination.Exploiting full-duplex capability, the Base-Station (BS) or Access Point(AP) can continually monitor its incoming signal in search for such arequest-to-join signal. Once such a signal is detected, the nodeallocates resources to the new client and synchronizes it with the rest(i.e., synchronization within the cyclic prefix of the underling OFDM).

To handle asynchronous clients, receiving node (e.g., AP) will be alwayslistening to detect a valid request-to-join signal, while supportingfull-duplex connections to its current clients. In one embodiment,several repetitions of a sequence (i.e., several periods of a periodicsequence) are used as the request-to-join signal. Once such a signalpasses through the linear system corresponding to the channel, itresults in an almost periodic sequence of the same period. This can bedetected at the receiver end by using a simple correlation calculationby sliding two consecutive windows of the length of that period,shifting them through the incoming signal sample by sample, andcomputing the inner product of the vectors within the two windows. Thisproduces a peak when the periodicity starts, and this peak will continueuntil the periodicity lasts. It should be ensured that the remainingamount of self-interference does not cause complete loss of thiscorrelation peak. Note that correlation calculation on its own providesa significant boost in signal to noise.

The possibility of supporting two-way links with multiple (initiallyasynchronous) clients helps with many of the current challenges ofwireless networks (cellular and WLAN). Examples are problems of MultipleAccess Control (MAC), resource allocation, Quality of Service (QoS),co-operative communications, interference management and scheduling.

Access to a return channel can be used in part (e.g., by allocating asubset of OFDM tones) to facilitate control signaling. This includessending pilots for time and/or frequency synchronization, ARQ, powercontrol, adaptive coding and modulation, etc. An important usagescenario in this category is the case of co-operative signaling. Inrecent years, there have been significant work on setups like broadcastchannel, multiple access channel and interference channel. Time andfrequency synchronization in such setups is a major issue. Access tofull-duplex links can facilitate practical implementation of suchsetups. In one embodiment, one node broadcasts a set of pilots to beused by all network nodes as a reference for their carrier. Anotherembodiment concerns a scenario that a large number of transmit antennas,each with low transmission power, are used to perform beam-forming inphase and/or polarization for a receiver which has a small number, andin particular, a single antenna.

Access to a return channel also enables the receiver to periodicallyfeedback the channel state (phase, magnitude and/or polarization)corresponding to each transmit antenna to be used by the multipleantenna transmitter for beam forming. This setup can be used to reducetransmit power, and in particular is useful in scenarios that transmitpower is limited due to regulatory considerations. In anotherembodiment, transmitting nodes gather an indication of the amount ofinterference in different frequency bands through listening whiletransmitting, and adjust their transmission parameters accordingly.

Possibility of supporting two-way links solves many of resourceallocation and scheduling issues that are currently prominentbottlenecks in cost effective and efficient realization of wirelessnetworks. This disclosure includes methods wherein interfering nodes, bylistening to each other while transmitting, can form a distributedcollaborative signaling scheme. For example, in the case of two-userInterference Channel (IC), the two transmitting nodes can listen to eachother during one symbol and then form a distributed space-time code,e.g., an Alamouti code, in the next symbol. This can be achieved bylistening to several symbols gathered in a coded block and use thisinformation (after partial or complete decoding of the coded block) tohelp in the following block(s). Likewise, the two transmitting nodes canlisten to each other during one coded block and then form a distributedAlamouti code in the next block. Such setups can be also useful inmultiple access scenarios, e.g., when two clients send data to an accesspoint. As an alternative to Alamouti code, transmitter/receiver nodescan adjust their transmission/detection strategies such that eachreceiver detects its own message, rather than detecting both messages.In the case that the receiver nodes are also full duplex, it is possibleto base the second phase (collaboration phase) on either the transmitter(as above) or the receiver. In other words, during the collaborationphase, either or both receivers relay their received message to theother receiver. This feature increases the achieved diversity gain. Forexample, in the case of two-user interference channel composed ofinterfering links T1=R1 and T2→R2, the following configurations can beused in the collaboration phase (T1,T2), (T1,R1), (T1,R2), (T2,R1), or(T2,R2).

Above cooperative setup can be used in the case of a multiple accesscannel (the two nodes send data to the same access point). In a moregeneral setup that multiple transmitter/receiver pairs share thespectrum, once a node has access to a data symbol relevant to the othernode(s), it can decide to activate its transmitter to relay the receivedsignal within the OFDM cyclic prefix, while continuing to listen tosubsequent incoming signals. This feature can be used to enhancediversity, or save energy through relaying operation (when the relayingnodes enjoy good outgoing channel conditions).

FIG. 4 are block diagrams showing cooperative communication inaccordance with one example. Unit A has a message intended to be sent toUnit A′ and Unit B has a message intended to be sent to Unit B′. Allreceivers hear transmitters. In a phase 1, transmitters in subunits in Aand B transmit their respective messages. This may include a singletransmission, or a coded block protected by Forward Error Correction(FEC). A phase 2 of co-operation starts after phase 1. All receivershear transmissions in phase 1 and phase 2, but a selected subset ofreceivers will be active and listen to the incoming signal. In FIG. 4,subunits specified in smaller boxes with bold-ace fonts specify subunitsthat are active in phase 1 and phase 2, either as transmitter or asreceiver. Direction of arrows in FIG. 4 show the flow of information inthe sense of specifying, which receive subunit, is listening to whichtransmit subunit. In phase 2, two transmit subunits and two receivesubunits are active. Active receive subunits are on the receive side,but active transmit subunits can be on either sides depending on thequality of their received signal in phase 1, which in turn is dictatedby the channel gains and respective signal-to-noise ratios in phase 1.This results in 4 protocols for phase 2 as shown in FIG. 4. A decisionabout which of these protocols should be followed in phase 2 can be madeby a central node, which informs all the units of the policy to be used.Such a policy can be revised in periods determined by how fast thechannel conditions are changing. As mentioned earlier, phase 1 can be asshort as a single transmission, and as long as a coded block protectedby FEC. Correspondingly, phase 2 will operate on the single symbol, oron the coded block. Phase 2 can relay the noisy signal, or performcomplete or partial decoding to remove or reduce the effect of thenoise. To reduce or remove noise, this operation involves hard decision,soft decision or soft output decoding. Accordingly, transmission policyof each transmit subunit active in phase 2, say in terms of transmitenergy, can be locally optimized according to the instantaneous qualityof the corresponding received signal in phase 1. These local adjustmentsto policy will be complementary to the global policy determined by thecentral node.

Traditional wireless networks rely on two types of links for exchange oftwo types of information, namely data and control. One type is to handlethe main bulk of data to be communicated (data link) and another type isto handle various control information (control link). Data link isusually of high throughput, and control link is usually of lowthroughput. A major bottleneck is to establish the control link in atimely manner without causing too much disturbance on the networkoperation. In current half-duplex networks, data and control links areestablished either using different frequency bands, or using differenttime slots. Existing solutions based on frequency division duplex areusually expensive, and existing solutions based on time division duplexare usually inefficient. For example, in 802.11, which is based on timedivision duplex, a new node which wants to transmit information (data orcontrol) has to wait until channel is idle. This is called Carrier SenseMultiple Access (CSMA) and is the main source of poor efficiency in802.11. With the wide spread use of smart phones, this problem isexpected to become more severe. The reason is that as smart phones movein areas covered by 802.11, they can easily get disconnected from theircurrent access point and subsequently try to get associated with anotheraccess point and this requires significant control signaling.Ironically, in most cases, the moving smart phones do not have anyactual data to send or receive, but their control signaling usuallyimposes overwhelming degradations in network delay and throughout. Itwill be useful if low throughput control links could be establishedasynchronously and in parallel with high throughput data links. In anembodiment, this is achieved by overlaying a network of low throughputcontrol links on top of the high throughput network of data links.Transmission on the Low Throughput Overlay (LTO) channel forming thecontrol links uses signaling schemes with low power and thereby lowspectral efficiency. For example, a transmitter can send several periodsof a periodic signal in time domain, which can be detected by a simplecorrelation calculation using sliding windows. The presence of such asignal indicates incoming control data, and the amplitude and/or phaseand/or duration of a basic periodic signal can be varied (with respect astarting periodic signal used as a preamble) to embed the control data.This may also include FEC with a short block length. Nodes, which areinterested to participate in the overlay control network, will sense theLTO channel and transmit if the channel is idle (can possibly use aback-off strategy similar to CSMA protocol used in 802.11). To avoidcollisions, there is provided a manner to indicate occupancy of the LTOchannel which shares (is overlaid on top of) the spectrum used for themain data network. Main data links operate with relatively higher powerover the High Throughout Main (HTM) channel. Using methods describedherein, this is achieved by searching for the basic periodic signal as asign of LTO channel being idle or occupied. Nodes involved in signalingover HTM channel can first search for the LTO signal, perform signaldetection on it, and then (partially or fully) cancel the LTO signal toreduce its harmful effect on the HTM channel. There is provided amethod, in the context of handing asynchronous clients, to establish aframework to implement the above setup of an LTO channel workingasynchronously and in parallel with the HTM channel withoutsignificantly degrading the HTM channel due to the inherent interferencebetween LTO and HTM channels due to the sharing of spectrum.

FIG. 5 is a flowchart showing a method with operations 400 for awireless communication device for establishing and/or handlingcommunications over an LTO channel asynchronously and in parallel withcommunications over an HTM data channel in accordance with oneembodiment. It will be understood that operations 402-404 relate to HTMdata channel communications and operations 406-422 relate to LTO channelcommunications. Respective operations may be performed by respectivesubunits of the wireless communication device. FIG. 5 applies to eitheraccess point, or client. In particular any unit which may get involvedin ad-hoc or mesh networking should have equal capabilities in thisrespect. However, in a simple network setup, clients may use the LTOchannel in the uplink to announce their presence, and then listen forresponse from the AP in the HTM channel.

At 402, a determination is made whether the communications are over theHTO. If no operations return to the start of operations 400. If yes,operations perform self-interference cancellation in frequency domain,OFDMA networking and transmit/receive operations, possiblydetecting/cancelling signal from LTO receive channel prior to decodingdata.

At 406, a determination is made whether data is received over LTOchannel. If yes, at 408, operations perform self-interferencecancellation in the time domain and receive data via the LTO channeluntil all data is received. If data is not received, there may be datato send over the LTO channel (determination at 410). If yes, at 412,operations perform self-interference cancellation in the time domain andsearch for the periodic sequence indicating if the LTO channel isoccupied. At 414 operations determine whether the LTO channel is idle(i.e. available for the communication device). If no, operations returnto 412 to try again. If yes, at 416 data is transmitted over the LTOchannel superimposed on the periodic signal indicating LTO channeloccupancy. At 418, a determination is made whether more data is to besent over the LTO channel. If yes, operations return to 416. If not, at420 the device performs self-interference cancellation in the timedomain and searches for the periodic sequence indicating if another node(device) wants to initiate communications over the LTO channel. If at422 there is no incoming communication over the LTO channel, operationsmay continue at 410. If yes, operations continue at 408 as previouslydescribed.

In the context of IC, this disclosure includes methods to cancel theinterference at a receiving node through filtering andsuper-imposing/relaying of the received signal. This feature makes itpossible to achieve a multiplexing gain of one in a two-user IC, whichis in contrast to the limit of ½ using traditional half-duplex radios.In particular, there is presented a setup in which each transmitterlisten to the incoming signal and forwards it (after proper filtering intime domain) to its respective receiver (on top of the desired signal)such that it cancels the interference signal arriving through the crosslink. To realize such a cooperative scheme, one needs to account for thedelay in exchanging information between transmitters. Methods describedherein use a minimum delay dictated by the channel memory as captured inOFDM cyclic prefix. In contrast, in the literature based on using adiscrete time model for the underlying channels, the minimum delay forcooperation is assumed to be limited to at least one symbol interval inthe discrete time axis. Relying on such a discrete time model limits thepotential gain due to such collaborations. The embodiments herein handlethe minimum delay requirement at a finer level of granularity. Thisexploits the fact that tolerance to transmission delay is governed byOFDM cyclic prefix, which is larger than the minimum delay requirementfor cooperation as governed by the underlying filtering/relayingoperation.

Another embodiment for the application of full-duplex link is a basicinterference channel (FIGS. 6 and 7) where there are transfer functionsG11, G12, G21, and G22 from the transmitters to the receivers, C12, C21for the links between them, and C11, C22 for the self-interference ofeach transmitter to itself In this setup, there is an interferencechannel that the transmitters want to collaborate and reduce the effectof their mutual interference. In Information Theatrical approaches, sucha collaboration is based on the assumption that transmit units requireto wait for one symbol (collaboration is restricted to have a delay ofat least one symbol). However, the methods herein exploit theobservation that relative delays within OFDM cyclic prefix (capturingchannel memory) are acceptable. Relying on this observation, to cancelthe interference at the distant receiver, transmitters TX1 and TX2 applya filter (in time domain) in the base-band of their receive chain, andforward the signal from the other node superimposed on their own signalsuch that it cancels the interference coming from the cross link.Receive filters should have the following expressions:

$R_{1} = \frac{G_{21}}{{G_{21}C_{11}} - {G_{11}C_{21}}}$ and$R_{2} = \frac{G_{12}}{{G_{12}C_{22}} - {G_{22}C_{12}}}$

Note that using such filters increases the transmit energy and therebyresults in decreasing the signal to noise ratio, but it will cancel theinterference, and consequently, the multiplexing gain is 1 instead of0.5 which is the limit for interference channel with half-duplex links.FIG. 7 shows a more detailed schematic view of units operating in thesame frequency band, which filter and super-impose/forward the signalreceived from each other to cancel (pre-compensate) the interference attheir intended receiver. Accordingly:

t1=R1r1+s1

t2=R2r2+s2

r1=C11t1+C21t2

r2=C12t1+C22t2

r1=G11t1+G21t2

r2=G12t1+G22t2

FIG. 7 models the above operations in base-band wherein s1 and s2 areinformation-bearing signals aimed from each transmitter to itsrespective receiver.

Another aspect of this disclosure concerns the situation that some orall the control signaling can affect the propagation environment insmall increments. In this case, relying on a full duplex link, thisdisclosure includes methods to form a closed loop between a transmitterand its respective receiver wherein the control signals (affecting thechannel impulse response) are adjusted relying on closed loop feedback,e.g., using methods known in the context of adaptive signal processing.Channel impulse response can be changed by modifying the RF propertiesof the environment external, but close, to the transmit and/or receiveantenna(s). The criterion in such adaptive algorithms can be maximizingdesired signal, and/or minimizing interference, and/or increasingfrequency selectivity for diversity purposes. In such a setup, stabilitymay be compromised due to closed loops. These are one local loop at eachnode (between transmitter and receiver in the same node due to theremaining self-interference) and the third one is the loop formedbetween transmitter/receiver of one node and receiver/transmitter of theother node. It should be clear to those skilled in the area thattransmit gain, receive gain and gains in local loops of the two unitscan be adjusted to avoid such undesirable oscillations.

In some embodiments, a method of operating a wireless communicationnetwork for establishing communication between a Central Node, e.g,Access Point (AP) , Base-station (BS), and respective multiple clientswith two-way wireless links, i.e., complete or partial overlap in timeas well as in frequency, the wireless communication node comprising aMultiple-Input Multiple-Output (MIMO) antenna system, the methodcomprising:

-   -   1) a new client is allowed to send a request-to-join signal        without prior coordination, and with overlap in time and        frequency with the existing clients, and wherein,    -   2) central node is continually listening to detect a valid        incoming request-to-join signal, or other forms of control        signaling, of any client while communicating with the multiple        clients of the existing network using full-duplex connectivity        for both data and control flow, and wherein    -   3) a first stage of base-band self-interference cancellation is        followed by an algorithmic base-band block, which works        synchronously with the transmit signal of a central node A to        detect the request-to-join signal and subsequently trigger a        sequence of operations required for the node B to join the        network associated with node A, or perform other network        management operation such as bandwidth allocation and        scheduling.

Alternative embodiments may include multiple clients connected to thecentral node sharing a common spectrum using Orthogonal FrequencyDivision Multiple Access (OFDMA). The method may include neighboringnodes, by listening to each other while transmitting, collaborating inthe subsequent transmission symbol(s), or collaborate in subsequenttransmission block(s). The method may include the use of part of areturn link as a control channel to, at least one of:

-   -   1) send pilots for synchronization;    -   2) coordinate retransmission of erroneous frames in ARQ without        severely interrupting a forward link;    -   3) coordinate adaptive coding and modulation and power control        based on the quality of the forward link, e.g., using channel        gain or features of observed multi-user interference across        frequency;    -   4) feedback the channel state (phase, magnitude, polarization)        in an asymmetric link wherein transmitter node posses many        antennas and rely on beam-forming in terms of channel state        (phase, magnitude, polarization) to achieve high reliability        with low transmit energy (e.g., below noise level); and,    -   5) feedback features of its received signal to improve the        capacity of the forward link in an interference channel.

The method of some further embodiments may include a central node usingpart of a forward link to broadcast a common pilot to be used by othernodes for synchronization and thereby enabling joint decoding in amultiple access channel or in an interference channel. Furtherembodiments may use a MIMO-SDMA network environment wherein part of areturn link from each receiver node is used to periodically feedback itscorresponding channel state, and wherein part of a forward link from amain transmitter node is used to periodically broadcast a common pilotfor synchronization. The methods of further embodiments include anetwork environment wherein nodes periodically listen while transmittingto measure features of their observed multi-user interference terms, forexample energy of interference in different frequency segments, andaccordingly adjust their transmit/receive strategies.

Embodiments may also include methods described above used in a networkenvironment wherein a plurality of nodes filter and forward respectivereceive signals by super-imposing on the respective transmit signals ofeach respective node such that the corresponding interference term(s) atthe respective intended receiver for a node is cancelled. The methodsmay use a 2-user interference channel wherein a transmit and/or areceive node filter and forward their received signal, including throughsuper-imposing it on their transmit signal if applicable, to cancel themulti-user interference at either or both of receiving nodes. The methodmay be generalized to more than 2 interfering nodes, wherein transmitand/or receive nodes rely on multiple antennas in order to cancel themulti-user interference terms from several interfering nodes.

Further methods may be used in a cognitive transmission network, wherein

-   -   1) primary users are distinguished by a signature signal, e.g.,        a periodic preamble, to be sent at the beginning of their        transmission, and wherein    -   2) primary users start transmission without attention to the        channel occupancy by the secondary users,    -   3) secondary users will be continually listening and searching        for the signature of the primary users, and, wherein    -   4) secondary users adjust their transmission parameters once the        signature of the primary users is detected, e.g., stop their        transmission and continue with the remaining part at a later        time when the network becomes once again available to secondary        users.

Additional methods may be used in a cognitive network, wherein

-   -   1) users are distinguished by a signature signal according to        their class of service, e.g., CDMA codes which are superimposed        on their main signal, and wherein    -   2) users check for the channel occupancy, detect the class of        the users using the channel, and adjust their transmission        strategy accordingly.

An embodiment includes a method for overlaying a network of LowThroughout Control (LTC) links on top of the High Throughout Main (HTM)data links with overlap in time and frequency, and wherein, to enablecancellation on the HTM channel, transmission on the LTO channel usessignaling schemes with low power and thereby low spectral efficiency.

These methods may be used where,

-   -   1) an LTO transmitter sends several periods of a periodic signal        in time domain, which are detected by a correlation calculation        using sliding windows, and wherein    -   2) the presence of such a signal indicates incoming control        data, and wherein    -   3) the amplitude and/or phase and/or duration of a basic        periodic signal are varied (with respect a starting periodic        signal used as a preamble) to embed the control data, and        wherein    -   4) data on LTO includes Forward Error Correction (FEC) with a        short block length.

To avoid collisions, some of the above methods may use:

-   -   1) an overlaid signature signal is used to indicate occupancy of        the LTO channel, and wherein    -   2) nodes which are interested to participate in the overlay        control network will sense the LTO channel and transmit if the        channel is idle, e.g., by searching for the basic periodic        signal as a sign of LTO channel being idle or occupied, and        wherein    -   3) LTO links use a back-off strategy, e.g., similar to the CSMA        protocol used in 802.11, among themselves, and wherein,    -   4) HTM links operate with relatively higher power, and wherein,    -   5) nodes involved in signaling over HTM links first search for        the LTO signal, detect its timing and synchronize with it,        perform signal detection on it, and then (partially or fully)        cancel the LTO signal to reduce its harmful interference effect        on their respective HTM link.

Further methods may rely on a full duplex link to form a closed loopbetween a transmitter and its respective receiver, wherein the controlsignals (affecting the channel impulse response) are adjusted relying onclosed loop feedback, e.g., using methods known in the context ofadaptive signal processing.

Many of the methods described above may be used even where at least oneof the clients does not have full-duplex capability.

Still further embodiments include a wireless communication nodeconfigured to perform a method according to any one of the previousmethod claims.

In the foregoing specification, specific embodiments have beendescribed. However, one of ordinary skill in the art appreciates thatvarious modifications and changes can be made without departing from thescope of the invention as set forth in the claims below. Accordingly,the specification and figures are to be regarded in an illustrativerather than a restrictive sense, and all such modifications are intendedto be included within the scope of present teachings.

The benefits, advantages, solutions to problems, and any element(s) thatmay cause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeatures or elements of any or all the claims. The invention is definedsolely by the appended claims including any amendments made during thependency of this application and all equivalents of those claims asissued.

Moreover in this document, relational terms such as first and second,top and bottom, and the like may be used solely to distinguish oneentity or action from another entity or action without necessarilyrequiring or implying any actual such relationship or order between suchentities or actions. The terms “comprises,” “comprising,” “has”,“having,” “includes”, “including,” “contains”, “containing” or any othervariation thereof, are intended to cover a non-exclusive inclusion, suchthat a process, method, article, or apparatus that comprises, has,includes, contains a list of elements does not include only thoseelements but may include other elements not expressly listed or inherentto such process, method, article, or apparatus. An element proceeded by“comprises . . . a”, “has . . . a”, “includes . . . a”, “contains . . .a” does not, without more constraints, preclude the existence ofadditional identical elements in the process, method, article, orapparatus that comprises, has, includes, contains the element. The terms“a” and “an” are defined as one or more unless explicitly statedotherwise herein. The terms “substantially”, “essentially”,“approximately”, “about” or any other version thereof, are defined asbeing close to as understood by one of ordinary skill in the art, and inone non-limiting embodiment the term is defined to be within 10%, inanother embodiment within 5%, in another embodiment within 1% and inanother embodiment within 0.5%. The term “coupled” as used herein isdefined as connected, although not necessarily directly and notnecessarily mechanically. A device or structure that is “configured” ina certain way is configured in at least that way, but may also beconfigured in ways that are not listed.

It will be appreciated that some embodiments may be comprised of one ormore generic or specialized processors (or “processing devices”) such asmicroprocessors, digital signal processors, customized processors andfield programmable gate arrays (FPGAs) and unique stored programinstructions (including both software and firmware) that control the oneor more processors to implement, in conjunction with certainnon-processor circuits, some, most, or all of the functions of themethod and/or apparatus described herein. Alternatively, some or allfunctions could be implemented by a state machine that has no storedprogram instructions, or in one or more application specific integratedcircuits (ASICs), in which each function or some combinations of certainof the functions are implemented as custom logic. Of course, acombination of the two approaches could be used.

Moreover, an embodiment can be implemented as a computer-readablestorage medium having computer readable code stored thereon forprogramming a computer (e.g., comprising a processor) to perform amethod as described and claimed herein. Examples of suchcomputer-readable storage mediums include, but are not limited to, ahard disk, a CD-ROM, an optical storage device, a magnetic storagedevice, a ROM (Read Only Memory), a PROM (Programmable Read OnlyMemory), an EPROM (Erasable Programmable Read Only Memory), an EEPROM(Electrically Erasable Programmable Read Only Memory) and a Flashmemory. Further, it is expected that one of ordinary skill,notwithstanding possibly significant effort and many design choicesmotivated by, for example, available time, current technology, andeconomic considerations, when guided by the concepts and principlesdisclosed herein will be readily capable of generating such softwareinstructions and programs and ICs with minimal experimentation.

The Abstract of the Disclosure is provided to allow the reader toquickly ascertain the nature of the technical disclosure. It issubmitted with the understanding that it will not be used to interpretor limit the scope or meaning of the claims. In addition, in theforegoing Detailed Description, it can be seen that various features aregrouped together in various embodiments for the purpose of streamliningthe disclosure. This method of disclosure is not to be interpreted asreflecting an intention that the claimed embodiments require morefeatures than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive subject matter lies in less than allfeatures of a single disclosed embodiment. Thus the following claims arehereby incorporated into the Detailed Description, with each claimstanding on its own as a separately claimed subject matter.

We claim:
 1. A method comprising: in a full duplex transceiver,transmitting a first transmit message to a first receiver whilesimultaneously receiving a first receive message from a second fullduplex transceiver, wherein the first receive message is intended for asecond receiver; in the full-duplex transceiver, transmitting in a nexttime duration a retransmission of the first receive message to thesecond receiver superimposed with a second transmit message addressed tothe first receiver.
 2. The method of claim 1 wherein the first transmitmessage and the first receive message are coded blocks of data.
 3. Themethod of claim 1 wherein the retransmission of the first receive signalis relaying a noisy version of the receive signal;
 4. The method ofclaim 1 wherein the retransmission of the first receive signal is basedon either a completely decoded or partially decoded first receivemessage to remove or reduce the effect of the noise.
 5. The method ofclaim 4 wherein, to reduce or remove noise, the decoding is based on oneof: hard decision decoding, soft decision decoding or soft outputdecoding.
 6. The method of claim 1 further comprising determining aretransmission policy for a plurality of full duplex transceivers forretransmitting the first receive message from a third full duplextransceiver.
 7. A method comprising: in a full duplex transceiver,transmitting a first transmit message to a first receiver whilesimultaneously receiving a first receive message from a second fullduplex transceiver, wherein the first receive message is intended for asecond receiver; in the full-duplex transceiver, receivingretransmission policy information and responsively transmitting in anext time duration a retransmission of the first receive message to thesecond receiver superimposed with a second transmit message addressed tothe first receiver.
 8. The method of claim 7 wherein the retransmissionof the first receive signal is relaying a noisy version of the receivesignal;
 9. The method of claim 7 wherein the retransmission of the firstreceive signal is based on either a completely decoded or partiallydecoded first receive message to remove or reduce the effect of thenoise.
 10. The method of claim 9 wherein, to reduce or remove noise, thedecoding is based on one of: hard decision decoding, soft decisiondecoding or soft output decoding.
 11. A method comprising: in a fullduplex transceiver, in a first signaling interval, receiving a firstreceive message addressed to the full duplex transceiver and a secondreceive message addressed to a second full duplex transceiver; in thefull-duplex transceiver, receiving retransmission policy information;and, responsively transmitting in a next time duration a retransmissionof the second receive message to a receiver of the second full duplexreceiver while simultaneously receiving a third receive message intendedfor the full duplex transceiver.
 12. The method of claim 11 wherein theretransmission of the second receive message is relaying a noisy versionof the second receive message;
 13. The method of claim 11 wherein theretransmission of the second receive message is based on either acompletely decoded or partially decoded first receive message to removeor reduce the effect of the noise.
 14. The method of claim 13 wherein,to reduce or remove noise, the decoding is based on one of: harddecision decoding, soft decision decoding or soft output decoding.